Induced resistance and differential allocation of herbivore defensive chemicals: a case study with internode borer Chilo sacchariphagus indicus (Kapur) in sugarcane

Abstract

Methyl jasmonate (MeJA), a known resistance inducer molecule, when applied was found to give protection against the attack of internode borer (INB) Chilo sacchariphagus indicus (Kapur) (Lepidoptera: Crambidae) in sugarcane to the extent of 86.67% as against 73.33% damage in control plants. Estimation of 12 phenolic compounds in leaf and stem tissues, following external application of 100 ppm MeJA, indicated wide variation with a 19-fold higher production in leaf than in stem tissue implying differential allocation of these chemicals within by the plant. Among all the phenolics, ferulic acid was expressed at the highest levels in both leaf and stem tissues. Such differential allocation of defensive chemicals is resorted to by the host plant to economize its resources by directing the chemicals to the site of initial attack, i.e. leaf tissue in the present case, rather than systemically deploying throughout the plant. From the observations, reduced INB attack and production of phenolics under the influence of MeJA, it is hypothesized that plant recognizes feeding by herbivores in their early stages and triggers differential production of defensive chemicals to target the early and vulnerable stage of the pest to limit losses.

Keywords

• sugarcane
• internode borer
• induced resistance
• methyl jasmonate
• phenolic compounds